Chromatography is a set of techniques for separating a mixture into its constituents. In a liquid chromatography system, a pump takes in and delivers a high-pressure mixture of liquid solvents to an autosampler, where a sample within a sample loop awaits the arrival of the solvent stream. In an isocratic chromatography application, the composition of the liquid solvents remains unchanged, whereas in a gradient chromatography application, the solvent composition varies over time. After the mixture's arrival, to introduce the sample to the solvent stream, the autosampler switches an injector valve to place the sample loop in the path of the flowing mixture. The mobile phase, comprised of the sample dissolved in the solvent stream, then passes to a column of particulate matter, referred to as the stationary phase. By passing the mobile phase through the column, the various components in the sample separate from each other at different rates and thus elute from the column at different times. A detector receives the elution from the column and produces an output from which the identity and quantity of the analytes may be determined.
With high-pressure liquid chromatography systems, however, introducing a sample at low pressure into a high-pressure solvent stream can cause a significant pressure drop in the system. Moreover, aspirating the sample into the sample loop with air gaps in order to mitigate sample dispersion can exacerbate the pressure drop. Such pressure drops can produce undesirable deficits in delivered flow, thus negatively affecting the quality and reliability of the chromatographic outcome.